Contactless dimensional measurement by laser beam scanning

Accurate dimensional measurement is a stringent demand of today technology. Sometimes, the measurement is difficult because the body under test is not touchable. A modern solution of these two problems is contactless dimensional measurement by laser beam scanning. A moving mirror, driven by a scanner, reflects the incident He-Ne laser beam and forces it to describe a plane. A collimator transforms the plane in a parallel one, which defines the measuring field. When the test body is in the measuring field, it generates a shadow area, with a length proportional to the dimension of the body. This light distribution focuses on the surface of a photo-detector and then the electronic system processes it in order to display the results of the measurement. To prove this method, a set-up has been developed; its block-diagram is presented and the preliminary results are reported. Measuring range is (2 - 75) mm, resolution is of 1 micrometers and the accuracy is +/- 10 micrometers (2 (sigma) ).